Chemistry Reference
In-Depth Information
was thought to be due to microincineration, i.e., intense heating of the contaminants in
a time too short to appreciably heat the glass container [102]. In the following years,
many investigations using plasmas at low, medium, and atmospheric pressure
∗
in dif-
ferent configurations and gases, including gas mixtures commonly used for etching,
were carried out. In the 1980s,
plasma-assisted
gas sterilization systems working at
medium pressure were developed and commercialized. In these process, gases with
biocidal properties of their own are used, while
plasma-based
decontamination and
sterilization refer to plasma-activated processes in otherwise nonbiocidal gases. Since
the 1990s, an increasing number of studies on atmospheric pressure discharges (e.g.,
barrier discharges, plasma jets) for biological decontamination have been registered.
For further details on low- and medium-pressure plasma sterilization, the reader is
referred to the review articles of Moisan et al. and Lerouge et al. [102-104]. Com-
prehensive reviews on the activities at atmospheric pressure, including descriptions
of the plasma sources, can be found in the articles of Boudam et al. [105], Ehlbeck
et al. [106], and Laroussi ([107], chapters 9.9 in [26] and 32 in [108]).
This chapter will focus on the elementary processes of antimicrobial treat-
ment by means of nonthermal plasmas. First, some definitions and basics will be
introduced (Section 8.2.1.2.2). The elementary processes will be summarized and
discussed in Section 8.2.1.2.3. Finally, some selected examples on plasma-based
and plasma-assisted processes for antimicrobial surface treatment will be given
(Section 8.2.1.2.4). Tissue processing as well as water and gas decontamination
are outside the scope of this chapter. To inform about therapeutic applications, the
reviews of Stoffels (chapters 9.10 in [26] and 33 in [108]), Fridman et al. [98] and
Kong [99] are recommended, see also Section 8.2.2.4. For gas decontamination see,
e.g., [109-111] and section 8.2.3.1.6.
8.2.2.2 Some Basics of Biological Decontamination and Sterilization
8.2.2.2.1 Classification and Terms
Biological decontamination means the inactivation or removal of biological material,
including microorganisms, pyrogens, fungi, viruses, and even prions. One aspect is
the antimicrobial treatment, defined as
the inactivation of microorganisms with the
purpose to reduce infections
. Thus, antimicrobial treatment is a collective term for
disinfection
,
sterilization
, and
aseptic
as well as
antiseptic
, which all have different
definitions. Disinfection means
to put dead or living material in a situation where
it is not longer able to contaminate
. The practical advice of the national authorities
for conforming disinfection is a measurable reduction of pathogenic microorganisms
by at least a factor of 10
5
. Sterilization is strictly defined as
the complete absence of
viable microorganisms
. Since this cannot be proven experimentally, a sterility assur-
ance level (SAL) of 10
−
6
has been defined for practical purposes, i.e., an assurance
of less than one chance in one million that viable microorganisms are present in
products after sterilization is required [112]. However, since the maximum detec-
tion limit of microbiological tests is practically at 10
−
2
microorgamisms per object,
a measurable reduction of 10
6
steps is instructed (with doubling of intensity to fulfill
∗
Pressure ranges: low pressure: 0.1
...
...
100 Pa; medium pressure: 100 Pa
3.000 Pa; atmospheric
pressure: 101 325 Pa
=
1013.25 mbar.
